Three electroluminescent materials (for red, green and blue) are employed to realize a full-colored OLED display. The important issue is to develop red, green and blue electroluminescent materials with high efficiency and long life, in order to enhance the overall feature of the organic electroluminescent (EL) devices. The EL materials are classified into host materials and dopant materials from the aspect of their functions. It is generally known that a device structure having the most excellent EL properties can be fabricated with an EL layer prepared by doping a dopant to a host. Recently, development of organic EL devices with high efficiency and long life comes to the fore as an urgent subject, and particularly urgent is development of a material with far better EL properties as compared to conventional EL materials as considering EL properties required for a medium to large sized OLED panel. From this point of view, development of host material is one of the most important issues to be settled. The desired properties for the host material (serving as a solvent and energy conveyer in solid state) are high purity and appropriate molecular weight to enable vapor-deposition in vacuo. In addition, glass transition temperature and thermal decomposition temperature should be high enough to ensure thermal stability. Further, the host material should have high electrochemical stability for providing long life. It is to be easy to form an amorphous thin film, with high adhesiveness to other materials of adjacent layers but without interlayer migration.
In the meanwhile, for conventional blue materials, a number of materials have been developed and commercialized since the development of diphenylvinyl-biphenyl (DPVBi) (Compound a) by Idemitsu-Kosan. In addition to the blue material system from Idemitsu-Kosan, dinaphthylanthracene (DNA) (Compound b) of Kodac, tetra(t-butyl)perylene (Compound c) system or the like have been known. However, extensive research and development should be performed with respect to these materials. The distryl compound system of Idemitsu-Kosan, which is known to have highest efficiency up to now, has 6 lm/W power efficiency and beneficial device lifetime of more than 30,000 hr. However, when it is applied to a full-colored display, the lifetime is merely several thousand hours, owing to decrease of color purity over operation time. In case of blue electroluminescence, it becomes advantageous from the aspect of the luminous efficiency, if the electroluminescent wavelength is shifted a little toward longer wavelength. However, it is not easy to apply the material to a display of high quality because of unsatisfactory color purity in blue. Furthermore, the research and development of such materials are urgent because of the problems in color purity, efficiency and thermal stability.

In order to develop a host material with high efficiency and long life, compounds based on different backbones have been disclosed, such as dispiro-fluorene-anthracene (TBSA), ter-spirofluorene (TSF) and bitriphenylene (BTP). These compounds, however, did not result in color purity and luminous efficiency at a sufficient level.

The compound TBSA as reported by Gyeongsang National University and Samsung SDI (Kwon, S. K. et al., Advanced Materials, 2001, 13, 1690; Japanese Patent Laid-Open No. 2002121547), showed luminous efficiency of 3 cd/A at 7.7 V, and relatively good color coordinate of (0.15, 0.11), but it was applied as a material for a single layer, being inappropriate for practical use. The compound TSF reported by Taiwan National University (Wu, C.-C. et al., Advanced Materials, 2004, 16, 61; US Patent Publication No. 2005040392) showed relatively good external quantum efficiency of 5.3%, but it was still inappropriate for practical use. The compound BTP reported by Chingwha National University of Taiwan (Cheng, C.-H. et al., Advanced Materials, 2002, 14, 1409; US Patent Publication No. 2004076852) showed luminous efficiency of 2.76 cd/A and relatively good color coordinate of (0.16, 0.14), but this was still insufficient for practical use.
As described above, conventional materials are constituted of a single layer, not forming a host-dopant thin layer, and is difficult to be used practically from the aspect of color purity and efficiency. There are not enough data reliable, with respect to its long life.
In the meanwhile, according to a patent application of Mitsui Chemicals (Japan) (U.S. Pat. No. 7,166,240), the compounds shown below have the absorption spectra at 390 to 430 nm, with luminous efficiency of 4.6 cd/A. However, on the basis of these data, the compounds with above absorption wavelength range, electroluminescence of greenish blue color is anticipated, and the Patent Publication also indicates the color as bluish green color.
Particularly, embodiment of pure blue color is impossible with the symmetrical structure of the Patent Publication, and the material, which cannot provide pure blue luminescence, is inadequate to be practically applied to a full-colored display.
